Aqueous ink for inkjet printing

Abstract

Provided is a water-based ink for ink-jet printing, which is excellent in wet spreadability on a low-liquid absorbing printing substrate, and is excellent in suppression of mottling and suppression of occurrence of white spots on a printed material.SOLUTION: A water-based ink for ink-jet printing on a low-liquid absorbing printing substrate, which comprises a pigment, an organic solvent (A), at least two kinds of polyether-modified silicone-based surfactants having an HLB value of not less than 1.0 and not more than 7.0, and water, in which an octanol-water partition coefficient logP of the organic solvent (A) is not less than 0.10.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink for ink-jet printing. [Background technology]

[0002] Inkjet printing involves ejecting ink droplets from minute nozzles and depositing them directly onto a printing substrate to produce printed matter bearing characters and images. This printing method has become extremely popular due to its numerous advantages, including the ease and cost-effectiveness of producing full-color prints, the ability to use a variety of printing substrates, including plain paper, label paper, and plastic film, and the fact that it is non-contact with the printing substrate. In particular, inks that use pigments as colorants are becoming mainstream, due to their superior weather resistance and water resistance.

[0003] For example, Patent Document 1 discloses an aqueous inkjet ink that contains a pigment (A), a water-soluble acrylic urethane resin (B), a water-soluble organic solvent (C), a surfactant (D), and water, and that satisfies all of the specified conditions, with the aim of providing an aqueous inkjet ink that can provide printed matter with excellent image quality and color development, regardless of the type of paper substrate to be printed on, and that has excellent ejection stability. Furthermore, Patent Document 2 discloses a liquid ejection device that aims to provide a liquid ejection device that has good solid wettability and can effectively suppress uneven image density, and that includes a carriage equipped with a head that ejects liquid onto an object to be ejected, a drive unit that moves the carriage and the object to be ejected relatively, a measurement unit that measures the distance between the carriage and the object to be ejected, an imaging unit that images the object to be ejected, and a setting unit that sets the ejection performance of the liquid from the head based on the measurement results of the measurement unit and the image obtained by imaging by the imaging unit, wherein the liquid is ink, and the ink contains water, an organic solvent, a colorant, and multiple polysiloxane compounds. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-60416 [Patent Document 2] Japanese Patent Application Publication No. 2019-155837 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, with the spread of digital printing, inkjet printing has been used not only for consumer and commercial printing but also for industrial printing using low-absorbency coated paper and non-absorbent resin film. In particular, because resin film substrates are hydrophobic, when aqueous inks are used, they have poor wetting and spreading properties, resulting in problems such as mottling (irregular variations in ink density) and poor filling of solid images during inkjet printing, resulting in reduced image quality. Therefore, to improve the wetting and spreading properties of the ink and suppress mottling, hydrophobic organic solvents and surfactants are sometimes blended into the ink. However, inks containing hydrophobic surfactants may not dissolve sufficiently in the ink, resulting in the occurrence of surfactant-induced white spots in the printed image, resulting in reduced image quality. Therefore, in order to improve the image quality of printed materials, it is necessary to improve the suppression of white spots on printed materials. However, the aqueous inkjet ink of Patent Document 1 was insufficient in wetting and spreading of the ink on a low-liquid-absorbent printing substrate and in suppressing mottle. Furthermore, although the ink described in Patent Document 2 has excellent wetting and spreading properties on low-liquid-absorbent printing substrates, it is insufficient in suppressing mottling and the occurrence of white spots on printed matter. An object of the present invention is to provide a water-based ink for inkjet printing that has excellent wetting and spreading properties on low-liquid-absorbent printing substrates and is excellent in suppressing mottling and the occurrence of white spots on printed matter, and an inkjet printing method that uses the water-based ink for inkjet printing. [Means for solving the problem]

[0006] The present inventors have discovered that the above-mentioned problems can be solved by providing a water-based ink for inkjet printing on a low-liquid-absorbent printing substrate, which contains a pigment, an organic solvent (A), at least two polyether-modified silicone surfactants having an HLB value of 1.0 or more and 7.0 or less, and water, wherein the organic solvent (A) has an octanol-water partition coefficient logP (hereinafter simply referred to as "logP") of 0.10 or more. That is, the present invention provides the following [1] and [2]. [1] A water-based ink for inkjet printing on a low-absorbency printing substrate, the ink contains a pigment, an organic solvent (A), at least two polyether-modified silicone surfactants having an HLB value of 1.0 or more and 7.0 or less, and water; the organic solvent (A) has an octanol-water partition coefficient log P of 0.10 or more; Water-based ink for inkjet printing. [2] An inkjet printing method, comprising printing on a low-liquid-absorbent printing substrate using the water-based ink for inkjet printing described in [1] above. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a water-based ink for inkjet printing that has excellent wetting and spreading properties on low-liquid-absorbent printing substrates and is excellent in suppressing mottling and the occurrence of white spots on printed matter, and an inkjet printing method that uses the water-based ink for inkjet printing. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Water-based ink for inkjet printing] The water-based ink for inkjet printing of the present invention (hereinafter also referred to simply as "water-based ink") is a water-based ink for inkjet printing on a low-liquid-absorbent printing substrate, and contains a pigment, an organic solvent (A), at least two polyether-modified silicone surfactants having an HLB value of 1.0 or more and 7.0 or less, and water. The organic solvent (A) has an octanol-water partition coefficient logP of 0.10 or more.

[0009] According to the present invention, it is possible to provide a water-based ink containing a pigment, an organic solvent, a surfactant, and water, which has excellent wetting and spreading properties on low-absorbency printing substrates and is excellent in suppressing mottling and the occurrence of white spots on printed matter. The reason for this is not necessarily clear, but is thought to be as follows. It is believed that the organic solvent (A) contained in the water-based ink of the present invention has a logP in a specific range, which allows the water-based ink of the present invention to sufficiently wet and spread even on hydrophobic, low-absorbency printing substrates that have low surface free energy. Furthermore, when a hydrophobic surfactant is blended into the ink, the surfactant may not dissolve sufficiently in the water-based ink, resulting in the appearance of surfactant-derived white spots on the printed matter and a deterioration in image quality. However, by blending an organic solvent (A) having a logP within a specific range, the hydrophobic polyether-modified silicone surfactant is dissolved in the water-based ink, which is thought to prevent the appearance of white spots on the printed matter. Furthermore, because the water-based ink contains at least two types of polyether-modified silicone surfactants as surfactants, phase separation of the surfactants is suppressed, which is thought to improve the effect of suppressing mottling. Furthermore, by sufficiently dissolving the polyether-modified silicone surfactant in the organic solvent (A) phase, it is expected that dispersion instability caused by collision of the solid surfactant with the pigment will be suppressed, thereby improving the storage stability of the ink.

[0010] The definitions of various terms used in this specification are shown below. "Containing component X" also means "composed of component X." "Aqueous" means that water accounts for the largest proportion by mass of the medium. The term "water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C in an amount of 5 mL or more. The term "low liquid absorption" in the context of low liquid absorption printing substrates refers to a concept that encompasses both low liquid absorption and non-liquid absorption, and refers to the amount of water absorption of the printing substrate when the printing substrate is in contact with pure water for 100 ms. 2 More than 10g / m 2The water absorption amount can be measured using an automatic scanning absorption meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) as the amount transferred when pure water is in contact for 100 ms under conditions of 23°C and a relative humidity of 50%. "Printing" is a concept that includes printing and printing out characters and images, and "printed matter" is a concept that includes printed matter and printed out matter on which characters and images are recorded.

[0011] <Pigments> The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and lake pigments and fluorescent pigments may also be used. If necessary, these pigments may also be used in combination with extender pigments. Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, and pearlescent pigments. Carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments. In the achromatic ink, achromatic pigments such as white, black, and gray can be used, while in the chromatic ink, chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred organic pigments include one or more product numbers selected from CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green. Examples of extender pigments include silica, calcium carbonate, and talc. The above pigments can be used alone or in combination of two or more.

[0012] From the viewpoint of print density, the content of the pigment in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less.

[0013] (pigment dispersant) In the aqueous ink of the present invention, the pigment is dispersed in the medium using a pigment dispersant. Examples of the pigment in the aqueous ink of the present invention include a form in which the pigment is dispersed using a resin (hereinafter also referred to as a "pigment dispersing resin") or a surfactant as the pigment dispersant. Among these, the form of the pigment in the aqueous ink of the present invention is preferably a form in which the pigment is dispersed using a pigment dispersing resin, and more preferably a form in which the pigment is contained in resin particles (hereinafter also referred to as "pigment-containing resin particles"). The form of the pigment-containing resin particles is not particularly limited, as long as they are formed from at least a pigment and a pigment dispersing resin, and are particles in which the pigment dispersing resin is adsorbed onto the pigment in the aqueous ink. Examples of the form of the pigment-containing resin particles include a form in which the pigment is encapsulated in the pigment dispersing resin, a form in which the pigment is uniformly dispersed in the pigment dispersing resin, a form in which the pigment is exposed on the surface of the pigment dispersing resin particles, and mixtures thereof.

[0014] (pigment dispersion resin) The pigment dispersing resin may be either a water-soluble resin or a water-insoluble resin. Here, regarding the "water-soluble" and "water-insoluble" of a resin, when a resin that has reached a constant weight after drying at 105°C for 2 hours is dissolved in 100 g of water at 25°C until saturation is reached, if the dissolved amount exceeds 10 g it is judged to be "water-soluble," and if it is 10 g or less it is judged to be "water-insoluble." Furthermore, as described below, if the pigment dispersion resin has anionic groups that are further neutralized with a neutralizer, the solubility is judged from the dissolved amount measured in the presence of a neutralizer such that the mass ratio of the pigment dispersion resin to the neutralizer is the same as that in the water-based ink of the present invention.

[0015] Examples of pigment dispersion resins include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); and condensation resins such as polyester resins and polyurethane resins. The pigment dispersion resin may be an appropriately synthesized product, or a commercially available product. Among these, the pigment dispersion resin is preferably one or more selected from the group consisting of vinyl resins, from the viewpoint of obtaining an ink that has excellent wetting and spreading properties and is excellent in suppressing mottling and the occurrence of white spots on printed matter.

[0016] The pigment dispersion resin may have a crosslinked structure. In this case, the pigment dispersion resin preferably has a structure including a resin having a linear two-dimensional structure that may have branched chains and a component derived from a crosslinking agent. It is believed that such a crosslinked structure is formed by a resin having a linear two-dimensional structure that may have branched chains being converted into a three-dimensional structure by a component derived from a crosslinking agent. Examples of resins having a linear two-dimensional structure that may have branched chains include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); condensation resins such as polyester resins and polyurethane resins; and the vinyl resins described below are preferred. The crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms, even more preferably one or more compounds selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether. When the crosslinking agent is a polyfunctional epoxy compound, the epoxy group equivalent weight of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, even more preferably 150 or less.

[0017] [Vinyl resin] From the viewpoint of improving the dispersion stability of the pigment, the vinyl resin used as the pigment dispersing resin preferably contains a structural unit derived from an anionic group-containing monomer. In this specification, the term "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include a carboxy group (-COOM), a sulfonic acid group (-SO3M), and a phosphate group (-OPO3M2). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Examples of vinyl resins include homopolymers of anionic group-containing monomers, copolymers of anionic group-containing monomers and hydrophobic monomers, and copolymers of anionic group-containing monomers, hydrophobic monomers, and nonionic monomers. Here, the term "hydrophobic" in the context of a hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of dissolution is less than 10 g. The nonionic monomer is a monomer that has a high affinity for water, such as a monomer that contains a hydroxy group or a polyalkylene glycol chain. When the vinyl resin is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer.

[0018] Examples of the anionic group-containing monomer include a carboxy group-containing monomer, a sulfonic acid group-containing monomer, and a phosphoric acid group-containing monomer. Among these, the carboxy group-containing monomer is preferred, and (meth)acrylic acid is more preferred. Examples of hydrophobic monomers include (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms; aromatic group-containing monomers such as styrene-based monomers and aromatic group-containing (meth)acrylates; and styrene-based macromonomers. The molecular weight of the aromatic group-containing monomer, preferably the styrene-based monomer, is preferably less than 500. The styrene-based macromonomer is a compound having a polymerizable functional group at one end and a number-average molecular weight of from 500 to 100,000. Among these, the hydrophobic monomer is preferably a (meth)acrylate or styrene-based monomer having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, more preferably one or more selected from the group consisting of alkyl (meth)acrylates having from 3 to 8 carbon atoms, styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, and even more preferably one or more selected from the group consisting of butyl acrylate, cyclohexyl acrylate, and styrene. Examples of nonionic monomers include polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate; and alkoxypolyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and octoxypolyethylene glycol mono(meth)acrylate. The term "(meth)acrylic acid" refers to at least one selected from the group consisting of acrylic acid and methacrylic acid, and the term "(meth)acrylate" refers to at least one selected from the group consisting of acrylate and methacrylate. Moreover, each of the monomers of the vinyl resin may be used alone or in combination of two or more.

[0019] When the vinyl resin is a copolymer, the vinyl resin preferably contains one or more structural units derived from anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, one or more structural units derived from hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, and one or more structural units derived from nonionic monomers selected from the group consisting of polyalkylene glycol mono(meth)acrylates and alkoxypolyalkylene glycol mono(meth)acrylates, and more preferably one or more structural units derived from anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid. and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers, and structural units derived from one or more nonionic monomers selected from the group consisting of polyalkylene glycol mono(meth)acrylates and alkoxypolyalkylene glycol mono(meth)acrylates, and more preferably structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers.

[0020] When the vinyl resin is a copolymer of an anionic group-containing monomer and a hydrophobic monomer, the content of the constituent units derived from each monomer component in all the constituent units of the vinyl resin is as follows. The content of structural units derived from anionic group-containing monomers in all structural units of the vinyl resin is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of improving the dispersion stability of the pigment and obtaining an ink that is excellent in wetting and spreading properties and is excellent in suppressing mottling and the occurrence of white spots on printed matter, and from the same viewpoints as above, is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. The content of structural units derived from hydrophobic monomers in all structural units of the vinyl resin is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more, from the viewpoint of improving the dispersion stability of the pigment and obtaining an ink that is excellent in wetting and spreading properties and is excellent in suppressing mottling and the occurrence of white spots on printed matter, and from the same viewpoints as above, is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. The vinyl resin can be obtained, for example, by addition polymerization of raw material monomers including an anionic group-containing monomer, a hydrophobic monomer, or a nonionic monomer by a known method.

[0021] From the viewpoint of improving the dispersion stability of the pigment, the acid value of the vinyl resin is preferably 40 mgKOH / g or more, more preferably 50 mgKOH / g or more, and even more preferably 60 mgKOH / g or more. From the same viewpoint as above, it is preferably 800 mgKOH / g or less, more preferably 500 mgKOH / g or less, and even more preferably 300 mgKOH / g or less. The acid value of the vinyl resin can be determined by the method described in the Examples, but it can also be calculated from the mass ratio of the constituent monomers. Furthermore, the acid value of a vinyl resin having a crosslinked structure can also be calculated using the following formula. Acid value of vinyl resin with crosslinked structure (mg KOH / g) = [Acid value of vinyl resin before crosslinking (mg KOH / g) x [(100 - crosslinking rate (mol%)) / 100]

[0022] The weight-average molecular weight of the vinyl resin is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more, from the viewpoints of pigment dispersion stability and obtaining an ink that is excellent in wetting and spreading properties and that is excellent in suppressing mottling and the occurrence of white spots on printed matter, and from the same viewpoints as above, is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The weight-average molecular weight of the vinyl resin can be measured by the method described in the Examples.

[0023] Commercially available vinyl resins include, for example, polyacrylic acids such as "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.); and styrene / acrylic resins such as "Joncryl 67," "Joncryl 611," "Joncryl 678," "Joncryl 680," "Joncryl 690," and "Joncryl 819" (all manufactured by BASF Japan Ltd.).

[0024] When the pigment in the water-based ink of the present invention is in the form of pigment-containing resin particles, the pigment-containing resin particles are preferably blended into the water-based ink as an aqueous dispersion (hereinafter also referred to as "pigment aqueous dispersion") obtained by dispersing the pigment, pigment dispersing resin, and, if necessary, a neutralizing agent, a surfactant, and the like, by a known method. A preferred method for producing a pigment aqueous dispersion is to disperse a pigment mixture containing a pigment, a pigment dispersing resin, an organic solvent, and water to obtain a dispersion, and then remove the organic solvent from the obtained dispersion. If necessary, a crosslinking agent may be further added to the obtained pigment aqueous dispersion to crosslink the pigment dispersing resin. Specific examples of such methods include those described in paragraphs

[0022] to

[0026] of JP-A-2022-104084. When the pigment is blended in the aqueous ink as a pigment aqueous dispersion, the average particle size of the pigment-containing resin particles in the aqueous dispersion is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more, from the viewpoints of dispersion stability of the pigment and of obtaining an ink that is excellent in wetting and spreading properties, suppressing mottling, and suppressing the occurrence of white spots in printed matter, and from the same viewpoints as above, is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less. The average particle size of the pigment-containing resin particles in the pigment aqueous dispersion can be measured by the method described in the Examples.

[0025] When the pigment is in the form of pigment-containing resin particles, the mass ratio of the pigment content to the total content of the pigment and pigment dispersant [pigment / (pigment+pigment dispersant)] is preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.6 or more, from the viewpoint of improving the dispersion stability of the pigment, and is preferably 0.9 or less, more preferably 0.8 or less, and even more preferably 0.75 or less, from the same viewpoint as above. When the pigment dispersant is a pigment dispersant resin that has been crosslinked with a crosslinking agent, the content of the pigment dispersant in the ink of the present invention is the total content of the pigment dispersant resin before crosslinking and the crosslinking agent.

[0026] <Organic solvents> The water-based ink of the present invention contains an organic solvent (A).

[0027] (Organic solvent (A)) The organic solvent (A) is a solvent having an octanol-water partition coefficient log P of 0.10 or more. The octanol-water partition coefficient logP of the organic solvent (A) is preferably 0.15 or more, more preferably 0.2 or more, from the viewpoint of obtaining an ink that has excellent wetting and spreading properties and is excellent in suppressing mottling and the occurrence of white spots on printed matter, and from the same viewpoint, is preferably 1.20 or less, more preferably 1.17 or less, and even more preferably 1.14 or less.

[0028] Examples of the organic solvent (A) include monoaliphatic ethers of alkylene glycols, monoaromatic ethers of alkylene glycols, and aliphatic alcohols.

[0029] Examples of the organic solvent (A) include monoaliphatic ethers of alkylene glycols such as diethylene glycol ethyl methyl ether (log P: 0.12), tripropylene glycol monomethyl ether (log P: 0.22), ethylene glycol monoisopropyl ether (log P: 0.23), dipropylene glycol dimethyl ether (log P: 0.41), diethylene glycol diethyl ether (log P: 0.45), diethylene glycol monoisobutyl ether (log P: 0.64), diethylene glycol monobutyl ether (log P: 0.67), propylene glycol monopropyl ether (log P: 0.71), ethylene glycol monoisobutyl ether (log P: 0.79), ethylene glycol monobutyl ether (log P: 0.81), dipropylene glycol monopropyl ether (log P: 0.88), and propylene glycol monobutyl ether (log P: 1.13), and ethylene glycol monoallyl ether (log P: 0.26). and aliphatic alcohols such as monoaromatic ethers of alkylene glycols, 3-methoxy-3-methylbutanol (logP: 0.11), 2-methylpentane-2,4-diol (logP: 0.17), 1,5-pentanediol (logP: 0.19), 1,2-pentanediol (logP: 0.43), 1,6-hexanediol (logP: 0.60), 1,2-hexanediol (logP: 0.85), and 2,3-dimethylbutane-2,3-diol (logP: 0.54). From the viewpoint of obtaining an ink that has excellent wetting and spreading properties and that is excellent in suppressing mottling and the occurrence of white spots on printed matter, the diol is preferably at least one selected from tripropylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monopropyl ether, propylene glycol monobutyl ether, 1,2-hexanediol, and 1,5-pentanediol. The organic solvent (A) may be used alone or in combination of two or more kinds.

[0030] From the viewpoint of obtaining an ink that has excellent wetting and spreading properties and that is excellent in suppressing mottling and the occurrence of white spots on printed matter, the content of the organic solvent (A) is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, and from the same viewpoint, the content is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 13% by mass or less.

[0031] (Organic solvent (B)) The water-based ink of the present invention preferably contains an organic solvent (B) other than the organic solvent (A). The organic solvent (B) can be appropriately selected depending on the purpose. Examples of the organic solvent (B) include water-soluble organic solvents such as polyhydric alcohols, glycol ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, the water-based ink preferably contains one or more organic solvents selected from polyhydric alcohols and glycol ethers as the organic solvent (B), from the viewpoint of obtaining an ink that has excellent wetting and spreading properties and is excellent in suppressing mottling and the occurrence of white spots on printed matter.

[0032] Examples of polyhydric alcohols include alkanediols such as ethylene glycol (logP: -1.36) and propylene glycol (logP: -0.92); polyalkylene glycols such as diethylene glycol (logP: -1.98), triethylene glycol (logP: -1.98), dipropylene glycol (logP: -0.82), and tripropylene glycol (logP: -0.38); glycerin (logP: -2.32); and trimethylolpropane (logP: -0.98). Examples of glycol ethers include ethylene glycol dimethyl ether (logP: -0.21), diethylene glycol dimethyl ether (logP: -0.36), and triethylene glycol dimethyl ether (logP: -0.52). Among these, the organic solvent (B) is preferably a polyhydric alcohol, more preferably an alkanediol, and even more preferably propylene glycol.

[0033] From the viewpoint of obtaining an ink that has excellent wetting and spreading properties and that is excellent in suppressing mottling and the occurrence of white spots on printed matter, the content of the organic solvent (B) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and from the same viewpoint, it is preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 25% by mass or less.

[0034] <Polyether-modified silicone surfactant> The polyether-modified silicone surfactant contained in the water-based ink of the present invention has an HLB value (Griffin method) of 1.0 or more, preferably 2.0 or more, more preferably 2.5 or more, and 7.0 or less, preferably 6.0 or less, more preferably 5.0 or less.

[0035] Polyether-modified silicone surfactants having an HLB value of 1.0 or more and 7.0 or less include compounds in which polyether groups are grafted onto a silicone main chain and compounds in which polyether groups are bonded in block form to both ends of a silicone main chain. Examples of the polyether group include polyethyleneoxy groups, polypropyleneoxy groups, and polyalkyleneoxy groups in which ethyleneoxy groups and propyleneoxy groups are added in block or random form. Preferred are polyether-modified silicone surfactants containing a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2), and optionally a structural unit represented by the following general formula (3). The structural unit represented by general formula (2) and / or the structural unit represented by general formula (3) contained in the polyether-modified silicone surfactant may be two or more types of the structural unit represented by general formula (2) and the structural unit represented by general formula (3).

[0036] [ka]

[0037] In the general formula (2), A represents an alkylene group having 1 to 4 carbon atoms, and R 1represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a trialkylsilyl group, and R 2 represents an alkyl group or a phenyl group having 4 to 20 carbon atoms, a is an integer of 0 to 30, and b is an integer of 1 to 30. In addition, in the structural unit represented by general formula (2), the structural unit represented by (CH(CH3)CH2O) and the structural unit represented by (CH2CH2O) may be interchanged in position, or may be repeated randomly.

[0038] Specific examples of the alkylene group having 1 to 4 carbon atoms, represented by A, include a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a propylene group, and a butylene group, and an ethylene group or a trimethylene group is preferred, and a trimethylene group is more preferred.

[0039] R 1 Specific examples of the alkyl group having 1 to 4 carbon atoms, represented by the formula (I), include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an s-butyl group, a t-butyl group, an isobutyl group, etc., and a methyl group or an ethyl group is preferred, and a methyl group is more preferred.

[0040] R 1 Specific examples of the trialkylsilyl group represented by the formula (I) include a trimethylsilyl group, a triethylsilyl group, a tri(n-propyl)silyl group, a triisopropylsilyl group, a tri(n-butyl)silyl group, and a dimethyl(t-butyl)silyl group, and are preferably a trimethylsilyl group or a triethylsilyl group, and more preferably a trimethylsilyl group.

[0041] R 2 The alkyl group having 4 to 20 carbon atoms represented by the formula (I) is preferably a linear or branched alkyl group having 10 to 20 carbon atoms, more preferably a linear alkyl group having 10 to 20 carbon atoms, and even more preferably a lauryl group or a cetyl group.

[0042] The number of repeating structural units represented by general formula (1) is preferably 20 or less, more preferably 10 or less, and even more preferably 5 or less. The repeating number b of the structural unit represented by general formula (2) is preferably 20 or less, more preferably 10 or less, and even more preferably 5 or less.

[0043] In the structural unit represented by general formula (2), the repeating number a of the structural unit represented by (CH(CH3)CH2O) is preferably 0 or more, and preferably 30 or less, more preferably 15 or less, and even more preferably 5 or less. In the structural unit represented by general formula (2), the repeating number b of the structural unit represented by (CH2CH2O) is preferably 1 or more, more preferably 3 or more, even more preferably 5 or more, and is preferably 30 or less, more preferably 20 or less, even more preferably 10 or less.

[0044] Specific examples of polyether-modified silicone surfactants with an HLB value of 1.0 or more and 7.0 or less include PEG-3 dimethicone (HLB value 4.5), PEG-9 methyl ether dimethicone (HLB value 4.5), PEG-10 dimethicone (HLB value 4.5), PEG / PPG-20 / 22 butyl ether dimethicone (HLB value 7.0), PEG-9 polydimethylsiloxyethyl dimethicone (HLB value 4.0), cetyl PEG / PPG-10 / 1 dimethicone (HLB value 3.5), and lauryl PEG-9 polydimethylsiloxyethyl dimethicone (HLB value 3.0). Examples of commercially available polyether-modified silicone surfactants having an HLB value of 1.0 or more and 7.0 or less include KF-6012 (HLB value 7.0), KF-6015 (HLB value 4.5), KF-6017 (HLB value 4.5), KF-6017P (HLB value 4.5), KF-6028 (HLB value 4.0), KF-6028P (HLB value 4.0), and KF-6048 (HLB value 3.5) manufactured by Shin-Etsu Chemical Co., Ltd.; Silface (registered trademark) SAG005 (HLB value 7.0) and Silface (registered trademark) SAG008 (HLB value 7.0) manufactured by Nissin Chemical Industry Co., Ltd.; and TEGO (registered trademark) Wet 270 (HLB value 3.0) and TEGO (registered trademark) Wet 3.0 manufactured by EVONIK. 280 (HLB value 3.5), BYK345 (HLB value 3.5) and BYK349 ​​(HLB value 4.0) manufactured by BYK Japan Co., Ltd.

[0045] The aqueous ink of the present invention contains at least two polyether-modified silicone surfactants having an HLB value of 1.0 or more and 7.0 or less. In the present invention, "different types of polyether-modified silicone surfactants" means that the respective structures are different. However, since polyether-modified silicone surfactants are generally mixtures of polymers containing structural units represented by general formula (1) and structural units represented by general formula (2), "different polyether-modified silicone surfactants" refers to the following cases: First, if the structural units contained in the respective polyether-modified silicone surfactants, for example, any one of the structural units represented by general formula (2) and the structural unit represented by general formula (3), are different, the respective polyether-modified silicone surfactants are different. Furthermore, if the number of repeating structural units represented by general formula (1) of the polyether-modified silicone surfactants differs by 0.3 or more when the number is 1 or more and 3 or less, by 1 or more when the number is more than 3 and 10 or less, by 1.5 or more when the number is more than 10 and 20 or less, or by 2 or more when the number is more than 20, the polyether-modified silicone surfactants are considered to be different. Furthermore, polyether-modified silicone surfactants are considered different if the repeating number of the structural unit represented by general formula (2) differs by 0.3 or more when it is 1 to 3, by 1 or more when it is more than 3 but 10, by 1.5 or more when it is more than 10 but 20, or by 2 or more when it is more than 20. Polyether-modified silicone surfactants containing only one of the structural units represented by (CH(CH3)CHO) and the structural unit represented by (CH2CHO) are considered different from polyether-modified silicone surfactants containing both structural units represented by general formula (2). Furthermore, polyether-modified silicone surfactants are considered different if the structural unit a represented by (CH(CH3)CHO) differs by 0 or more but 3 but 3, by 0.5 or more when it is more than 3 but 10, or by 1 or more when it is more than 10 but 30. Furthermore, in the structural unit represented by general formula (2), if the number b of structural units represented by (CH2CH2O) differs by 1 or more when it is more than 0 and 10 or less, or by 2 or more when it is more than 10 and 30 or less, the polyether-modified silicone surfactants are considered to be different. Furthermore, if the polyether-modified silicone surfactant differs by 0.3 or more when the number of repeating structural units represented by general formula (3) is 1 or more and 3 or less, by 1 or more when it is more than 3 and 10 or less, by 1.5 or more when it is more than 10 and 20 or less, or by 2 or more when it is more than 20, the polyether-modified silicone surfactants are considered to be different. The repeating number of each structural unit is a measured value of the polyether-modified silicone surfactant in the water-based ink, and can be measured by, for example, NMR. However, when the polyether-modified silicone surfactant is a random polymer, polyether-modified silicone surfactants that differ only in the order of the structural units are not considered to be different, whereas when the polyether-modified silicone surfactant is a block polymer, graft polymer, or the like, polyether-modified silicone surfactants that differ in the order of the structural units are considered to be different.

[0046] Regardless of the above, when commercially available polyether-modified silicone surfactants are used, the polyether-modified silicone surfactants contained therein are considered to be one type. However, commercially available products with the same main ingredient, such as the same polyether-modified silicone surfactant from different manufacturers, are considered to be the same polyether-modified silicone surfactant. When using a mixture of polyether-modified silicone surfactants, such as commercially available polyether-modified silicone surfactants, the differences between the commercial products are determined by comparing the analytical values ​​of the polyether-modified silicone surfactants contained in each commercial product as described above to determine whether they are identical or different. In the analytical values ​​for commercial products, the repeating number of each structural unit is calculated as the average value for the mixture of polyether-modified silicone surfactants included. Therefore, the calculated repeating number is limited to two significant digits. For example, we will explain the difference between BYK345 and BYK349 ​​manufactured by BYK Japan Co., Ltd. below. BYK345 has a repeating number of the structural unit represented by general formula (1) of 1.6, a repeating number of the structural unit represented by general formula (2) of 2.3, a is 0.36, and b is 6.0, while BYK349 ​​has a repeating number of the structural unit represented by general formula (1) of 1.3, a repeating number of the structural unit represented by general formula (2) of 1.7, a is 0.40, and b is 9.2. Therefore, BYK345 and BYK349 ​​can be determined to be different because the repeating number of the structural unit represented by general formula (1) is 1 or more and 3 or less, the difference being 0.3, the repeating number of the structural unit represented by general formula (2) is 1 or more and 3 or less, the difference being 0.6, and in the structural unit represented by general formula (2), the number b of the structural unit represented by (CHCHO) is 0 or more and 10 or less, the difference being 1 or more.

[0047] The content of the polyether-modified silicone surfactant having an HLB value of 1.0 or more and 7.0 or less is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, from the viewpoint of obtaining an ink that has excellent wetting and spreading properties and is excellent at suppressing mottling and the occurrence of white spots on printed matter, and from the same viewpoint, is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.8% by mass or less.

[0048] <Fixing resin> The water-based ink of the present invention may further contain a fixing resin. From the viewpoint of improving abrasion resistance and water resistance, the fixing resin preferably has a carboxyl group (-COOM). The carboxyl group is a group that exhibits acidity by dissociating and releasing a hydrogen ion, or a group in the dissociated ionic form (-COOM). - In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium, as in the anionic group described above.

[0049] From the viewpoint of improving abrasion resistance and water resistance, the acid value of the fixing resin is preferably 3 mgKOH / g or more, more preferably 5 mgKOH / g or more, and even more preferably 10 mgKOH / g or more, and from the same viewpoint as above, it is preferably 30 mgKOH / g or less, more preferably 25 mgKOH / g or less, and even more preferably 20 mgKOH / g or less. The acid value of the fixing resin can be determined by the method described in the examples, but it can also be determined by calculation from the mass ratio of the constituent monomers.

[0050] Examples of fixing resins include vinyl resins such as (meth)acrylic resins, styrene resins, styrene / (meth)acrylic resins, butadiene resins, styrene / butadiene resins, vinyl chloride resins, vinyl acetate resins, and acrylic silicone resins; polyurethane resins; and polyester resins. Note that "(meth)acrylic" refers to acrylic or methacrylic. Furthermore, when the fixing resin is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer. Among these, from the viewpoint of improving abrasion resistance and water resistance, the fixing resin is preferably one or more selected from the group consisting of vinyl resins having carboxy groups, polyurethane resins having carboxy groups, and polyester resins having carboxy groups, and more preferably vinyl resins having carboxy groups.

[0051] The vinyl resin having a carboxy group used in the present invention preferably contains a structural unit derived from a carboxy group-containing monomer and a structural unit derived from a hydrophobic monomer. The carboxy group-containing monomer is preferably (meth)acrylic acid. Preferred examples of the hydrophobic monomer include those exemplified for the vinyl resin used as the pigment dispersant. Among these, the hydrophobic monomer is preferably at least one selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene macromers, more preferably at least one selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers, even more preferably (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, still more preferably (meth)acrylates having an alkyl group having from 1 to 12 carbon atoms, and still more preferably (meth)acrylates having an alkyl group having from 1 to 8 carbon atoms. Each of the monomers of the vinyl resin having a carboxy group can be used alone or in combination of two or more.

[0052] The vinyl resin having a carboxy group preferably contains structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, more preferably contains structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers, and even more preferably contains structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid. The (meth)acrylic resin is a (meth)acrylic resin containing structural units derived from a carboxy group-containing monomer and structural units derived from a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, and even more preferably a (meth)acrylic resin containing structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid and structural units derived from a (meth)acrylate having an alkyl group having from 1 to 12 carbon atoms, and even more preferably a (meth)acrylic resin containing structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid and structural units derived from a (meth)acrylate having an alkyl group having from 1 to 8 carbon atoms, and even more preferably a copolymer of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate.

[0053] When the vinyl resin having a carboxy group is a copolymer of a carboxy group-containing monomer and a hydrophobic monomer, the content of the constituent units derived from each monomer component in the vinyl resin is as follows. The content of structural units derived from carboxyl group-containing monomers in the vinyl resin having a carboxyl group is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of improving abrasion resistance and water resistance, and from the same viewpoint as above, is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. The content of structural units derived from hydrophobic monomers in the vinyl resin having a carboxy group is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, from the viewpoint of improving abrasion resistance and water resistance, and from the same viewpoint as above, is preferably 99.5% by mass or less, more preferably 99% by mass or less, and even more preferably 98% by mass or less.

[0054] The weight-average molecular weight of the vinyl resin having a carboxy group is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 30,000 or more, still more preferably 50,000 or more, and even more preferably 100,000 or more from the viewpoint of improving abrasion resistance and water resistance, and is preferably 1,500,000 or less, more preferably 1,000,000 or less, and even more preferably 800,000 or less from the same viewpoint as above. The weight-average molecular weight can be measured by the method described in the Examples. The vinyl resin having a carboxy group is produced by polymerizing raw material monomers by a known polymerization method, such as emulsion polymerization or suspension polymerization, with emulsion polymerization being more preferred.

[0055] The polyurethane resin having a carboxy group used in the present invention is preferably a polyaddition product of an organic compound (polyol) component having two or more alcoholic hydroxyl groups in the molecule, including a dialkanolcarboxylic acid, and a polyisocyanate component. Examples of dialkanolcarboxylic acids include dimethylolbutanoic acid, dimethylolpropionic acid, and salts thereof. Among these, dimethylolpropionic acid is preferred.

[0056] The polyol component is not particularly limited as long as it is a compound having two or more alcoholic hydroxyl groups in the molecule, and examples thereof include polycarbonate-based polyols, polyester-based polyols, and polyether-based polyols. Examples of the polyisocyanate component include chain aliphatic diisocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; aliphatic diisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate and tetramethylxylylene diisocyanate; aromatic diisocyanates such as tolylene diisocyanate and diphenylmethane diisocyanate; and modified products of these diisocyanates (carbodiimide-, uretdione-, and uretoimine-containing modified products, etc.).

[0057] From the viewpoint of improving abrasion resistance and water resistance, the polyurethane resin having a carboxy group is more preferably a polyaddition product of dimethylolpropionic acid and a polycarbonate polyol as the polyol component and dicyclohexylmethane 4,4'-diisocyanate as the polyisocyanate component.

[0058] Examples of solvents used in the polyaddition reaction include acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, ethyl acetate, toluene, and xylene. In the polyaddition reaction, a chain extender or a reaction terminator may be used in combination, if necessary. The use of a chain extender can further increase the molecular weight. Examples of chain extenders include polyols and polyamines, and examples of reaction terminators include monoalcohols and monoamines.

[0059] In terms of dispersion stability in aqueous inks, it is preferable that at least a portion of the carboxy groups of the vinyl resin having a carboxy group, the polyurethane resin having a carboxy group, and the polyester resin having a carboxy group be neutralized with a neutralizing agent. Examples of the neutralizing agent include alkylamines such as butylamine and triethylamine; alkanolamines such as monoethanolamine, diethanolamine and triethanolamine; and inorganic bases such as morpholine, ammonia and sodium hydroxide.

[0060] Commercially available dispersions of vinyl resin particles having carboxy groups that do not contain pigments include, for example, acrylic resins such as "Neocryl A-1127" (trade name, anionic self-crosslinking aqueous acrylic resin, manufactured by DSM Coating Resins), "Joncryl 390," "Joncryl 7100," "Joncryl 7600," "Joncryl 537J," "Joncryl PDX-7164," "Joncryl 538J," and "Joncryl 780" (trade names, manufactured by BASF Japan Ltd.); styrene / butadiene resins such as "SR-100" and "SR102" (all trade names, manufactured by Nippon A&L Inc.); and vinyl chloride resins such as "Vinyblan 700" and "Vinyblan 701" (trade names, manufactured by Nissin Chemical Industry Co., Ltd.). Commercially available dispersions of polyurethane resin particles having carboxy groups that do not contain pigments include, for example, "NeoRez R-9603" (trade name, manufactured by DSM Coating Resins) and "WBR-2018" and "WBR-2000U" (trade names, manufactured by Taisei Fine Chemical Co., Ltd.). Commercially available dispersions of carboxyl-containing polyester resin particles that do not contain pigment include, for example, "ELITEL KA-5034," "ELITEL KA-5071S," "ELITEL KZA-1734," "ELITEL KZA-6034," "ELITEL KZA-1449," "ELITEL KZA-0134," and "ELITEL KZA-3556" (all of which are product names manufactured by Unitika Ltd.).

[0061] The fixing resin is preferably used as resin particles that do not contain a pigment, and from the viewpoint of improving the productivity of the water-based ink, it is preferably blended in the water-based ink as an aqueous dispersion of resin particles that do not contain a pigment. The fixing resin may be suitably synthesized or may be a commercially available product. When the fixing resin is formulated as an aqueous dispersion of pigment-free resin particles, the average particle size of the pigment-free resin particles in the aqueous dispersion is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more, from the viewpoint of ink storage stability, and is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less, from the same viewpoint as above. The average particle size of the pigment-free resin particles in the aqueous dispersion is measured by the method described in the Examples.

[0062] When the water-based ink of the present invention contains a fixing resin, the content of the fixing resin in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of obtaining an ink that has excellent wetting and spreading properties and is excellent in suppressing mottling and the occurrence of white spots on printed matter, and from the same viewpoint as above, is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less. When the pigment in the water-based ink of the present invention is in a form dispersed by a pigment dispersing resin, the mass ratio of the content of the fixing resin to the total content of the pigment dispersing resin and the fixing resin in the water-based ink of the present invention [fixing resin / (pigment dispersing resin+fixing resin)] is preferably 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, and is preferably 1.0 or less, more preferably 0.7 or less, even more preferably 0.5 or less.

[0063] <Water> The water-based ink of the present invention contains water. The water used in the water-based ink according to the present invention is preferably pure water or ion-exchanged water, from the viewpoint of preventing the inclusion of unintended substances.

[0064] The water content in the water-based ink is preferably 40% by mass or more, more preferably 45% by mass or more, and even more preferably 50% by mass or more, from the viewpoint of obtaining an ink that has excellent wetting and spreading properties and is excellent at suppressing mottling and the occurrence of white spots on printed matter, and from the same viewpoint as above, is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less.

[0065] The water-based ink of the present invention may further contain various additives, such as a humectant, wetting agent, wetting / penetrating agent, viscosity adjuster, antifoaming agent, preservative, antifungal agent, and antirust agent, if necessary.

[0066] [Method of manufacturing water-based ink for inkjet printing] The method for producing the water-based ink for inkjet printing of the present invention includes a step of mixing the pigment, the organic solvent (A), at least two polyether-modified silicone surfactants having an HLB value of 1.0 or more and 7.0 or less, and the water. During mixing, the fixing resin, surfactant, neutralizer, additives, etc. may be further added as needed. Mixing is preferably performed by blending and stirring the components of the water-based ink. When the pigment is in the form of pigment-containing resin particles, the pigment-containing resin particles are preferably blended after dispersing the pigment, pigment dispersing resin, and, if necessary, a neutralizing agent, a surfactant, and the like by a known method to obtain an aqueous dispersion of the pigment-containing resin particles, as described above.

[0067] (Physical properties of water-based inks for inkjet printing) The viscosity of the water-based ink of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 3.5 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, even more preferably 7 mPa·s or less. The viscosity of the water-based ink can be measured using an E-type viscometer. The pH of the water-based ink of the present invention is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher. From the viewpoints of component resistance and skin irritation, the pH is preferably 11 or lower, more preferably 10 or lower, and even more preferably 9.5 or lower. The pH of the water-based ink can be measured by a conventional method.

[0068] [Inkjet printing method] The inkjet printing method of the present invention is a method of printing on a low liquid-absorbent printing substrate using the above-mentioned water-based ink. In the inkjet printing method of the present invention, the method for ejecting the water-based ink is preferably a piezo type from the viewpoint of ejection properties.

[0069] (Low liquid absorption printing base material) Examples of low-liquid-absorbent printing substrates that can be used in the ink-jet printing method of the present invention include low-liquid-absorbent coated paper and resin films. Examples of low-liquid-absorbency coated paper include general-purpose glossy paper and multicolor foam glossy paper. Examples of the resin film include films made of synthetic resins. Examples of such synthetic resins include polyolefin resins such as polyethylene resins and polypropylene resins; polyester resins such as polyethylene terephthalate resins; and polyvinyl chloride resins. The resin film may be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film. Among these, the low-liquid-absorbent printing substrate is preferably a printing substrate made of a synthetic resin, and more preferably a low-liquid-absorbent printing substrate made of one or more synthetic resins selected from the group consisting of polyethylene resin, polypropylene resin, and polyethylene terephthalate resin. [Example]

[0070] In the following Production Examples, Examples, and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows. Pressure is expressed as absolute pressure.

[0071] (1) Measurement of the acid value of resin The resin was dissolved in a titration solvent (toluene:acetone = 2:1 (volume ratio)) mixed with toluene and acetone in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with 0.1 N potassium hydroxide / ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the endpoint. The acid value (mgKOH / g) was calculated from the titration volume of the potassium hydroxide solution up to the endpoint.

[0072] (2) Measurement of the weight average molecular weight of the resin The content was determined by gel permeation chromatography. The measurement sample was prepared by mixing 0.1 g of resin with 10 mL of the eluent described below in a glass vial, stirring with a magnetic stirrer at 25°C for 10 hours, and filtering with a syringe filter (Advantec Co., Ltd. "DISMIC-13HP" pore size: 0.2 μm, material: PTFE). The measurement conditions are shown below. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolumn Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits with known molecular weights, manufactured by Tosoh Corporation: "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)"

[0073] (3) Measurement of solids concentration of aqueous pigment dispersion and aqueous dispersion of fixing resin particles Approximately 10 g of sodium sulfate, brought to a constant weight in a desiccator, was weighed out into a 30 mL ointment container, and approximately 1 g of the sample was added and mixed, then weighed out and kept at 105°C for 2 hours to remove volatiles.The mixture was then left in the desiccator for a further 15 minutes, and the mass was then weighed out. The mass of the sample after volatile matter removal was taken as the solid content, and divided by the mass of the added sample to obtain the solid content concentration (%).

[0074] (4) Calculation of the octanol / water partition coefficient logP of organic solvents The log P of each organic solvent was calculated using ChemDraw Professional ver. 22.2.0.3300 (PerkinElmer).

[0075] (5) Calculation of HLB value of surfactant The HLB value indicates the affinity of a surfactant for water and oil, and was calculated by the Griffin method using the following formula: In the following formula, examples of the "hydrophilic group contained in the surfactant" include a hydroxyl group and an ethyleneoxy group. HLB = 20 × [(molecular weight of hydrophilic group contained in surfactant) / (molecular weight of surfactant)]

[0076] (6) Measurement of the average particle size of particles in water-based ink The water-based ink was subjected to cumulant analysis using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle diameter was measured as the average particle diameter of the particles in the water-based ink. The measurement sample had a particle concentration of 5 × 10 -3 The water-based ink was diluted with water to a concentration of 1.333 (solids content equivalent). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 integrations. The refractive index of water (1.333) was entered as the refractive index of the dispersion solvent.

[0077] (7) Measurement of viscosity of water-based ink The viscosity of the water-based ink at 32°C was measured using an E-type viscometer ("TV-25" manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1°34'×R24, rotation speed 50 rpm).

[0078] (8) Measurement of pH of water-based ink The pH of the water-based ink at 25°C was measured using a tabletop pH meter ("F-71" manufactured by Horiba Ltd.) equipped with a pH electrode ("6337-10D" manufactured by Horiba Ltd.).

[0079] Production Example 1 (Production of Pigment Water Dispersion 1) (1) Synthesis of pigment dispersing resin D1 A monomer mixture was prepared by mixing 31 parts of acrylic acid and 69 parts of styrene. A reaction vessel was charged with 10 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.2 parts of 2-mercaptoethanol (a polymerization chain transfer agent), and 10% of the monomer mixture, and the mixture was thoroughly purged with nitrogen gas. Meanwhile, a mixture of the remaining 90% of the monomer mixture, 0.2 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of an azo-based radical polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) was placed in a dropping funnel. The monomer mixture in the reaction vessel was heated to 65°C under a nitrogen atmosphere while being stirred, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 65°C from the end of the dropping, a solution of 0.1 parts of the polymerization initiator in 2 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and then at 70°C for 2 hours. The mixture was then dried under reduced pressure to partially remove the MEK, yielding an MEK solution (solids concentration 45%) of pigment dispersion resin D1 (acid value: 240 mgKOH / g, weight-average molecular weight: 13,900). 17.0 parts of the obtained MEK solution of pigment dispersion resin D1 was diluted with 4.9 parts MEK to a solids concentration of 35%. Next, 3.1 parts of a 5N NaOH aqueous solution was added so that the degree of neutralization of the carboxyl groups of pigment dispersion resin D1 was 40 mol%, and the mixture was stirred at 25°C. 75.0 parts of water was then added over 1 hour to cause phase inversion emulsification of pigment dispersion resin D1. After the addition was completed, the MEK was distilled off using an evaporator to obtain an aqueous dispersion of pigment dispersion resin D1 (solids concentration 25%).

[0080] (2) Preparation of Pigment Water Dispersion 1 To 32.97 parts of an aqueous dispersion of pigment dispersion resin D1 (solid content concentration 25%), 2.10 parts of MEK and 17.25 parts of ion-exchanged water were added, and 18.77 parts of a cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 Pigment Blue 15:3) was further added to obtain a pigment mixture. The resulting pigment mixture was mixed using a disper blade at 7000 rpm and 20°C for 1 hour, and then further dispersed using a Microfluidizer (high-pressure homogenizer, manufactured by Microfluidics, product name: M-140K) for 10 passes at a pressure of 180 MPa to obtain a pigment dispersion. From the resulting pigment dispersion, MEK was removed under reduced pressure at 60°C, and then some of the water was removed and centrifuged. The liquid phase was then filtered through a membrane filter (manufactured by Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding Pigment Water Dispersion 1 (solid concentration 22%, pigment: 15.4%, resin: 6.6%). The average particle size of the pigment-containing resin particles in Pigment Water Dispersion 1 was 105.3 nm.

[0081] Production Example 2 (Production of Pigment Water Dispersion 2) (1) Synthesis of pigment dispersing resin D2 A monomer mixture was prepared by mixing 26 parts of acrylic acid, 19 parts of butyl acrylate, and 55 parts of cyclohexyl acrylate. 10 parts of MEK, 0.2 parts of 2-mercaptoethanol (a polymerization chain transfer agent), and 10% of the monomer mixture were placed in a reaction vessel and mixed, followed by thorough nitrogen gas replacement. Meanwhile, a dropping funnel was charged with a mixture of the remaining 90% of the monomer mixture, 0.2 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of an azo-based radical polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65). Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 65°C with stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 65°C from the end of the dropping, a solution of 0.1 parts of the polymerization initiator in 2 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and then at 70°C for 2 hours. The mixture was then dried under reduced pressure to partially remove the MEK, yielding a MEK solution (solids concentration: 45%) of pigment dispersion resin D2 (acid value: 200 mgKOH / g, weight-average molecular weight: 16,100). 17.0 parts of the obtained MEK solution of pigment dispersion resin D2 was diluted with 4.9 parts MEK to a solids concentration of 35%. Next, 3.1 parts of a 5N aqueous solution of NaOH was added so that the degree of neutralization of the carboxyl groups of pigment dispersion resin D2 was 40 mol%, and the mixture was stirred at 25°C. 75.0 parts of water was then added over 1 hour to cause phase inversion emulsification of pigment dispersion resin D2. After the addition was completed, the MEK was distilled off using an evaporator to obtain an aqueous dispersion of pigment dispersion resin D2 (solids concentration 25%).

[0082] (2) Preparation of Pigment Water Dispersion 2 To 32.97 parts of an aqueous dispersion of pigment dispersion resin D2 (solid content concentration 25%), 2.10 parts of MEK and 17.25 parts of ion-exchanged water were added, and 18.77 parts of a cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 Pigment Blue 15:3) was further added to obtain a pigment mixture. The resulting pigment mixture was mixed using a disper blade at 7000 rpm and 20°C for 1 hour, and then further dispersed using a Microfluidizer (high-pressure homogenizer, manufactured by Microfluidics, product name: M-140K) for 10 passes at a pressure of 180 MPa to obtain a pigment dispersion. From the resulting pigment dispersion, MEK was removed under reduced pressure at 60°C, and then some of the water was removed and centrifuged. The liquid phase was then filtered through a membrane filter (manufactured by Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding Pigment Water Dispersion 2 (solids concentration 22%, pigment: 15.4%, resin: 6.6%). The average particle size of the pigment-containing resin particles in Pigment Water Dispersion 2 was 103.7 nm.

[0083] Production Example 3 (Production of Water Dispersion of Fixing Resin Particles) In a reaction vessel equipped with a dropping funnel, the monomers shown in "Initially charged monomer emulsion" in Table 1, LATEMULL E-118B (polyoxyethylene alkyl ether sodium sulfate, manufactured by Kao Corporation) as a surfactant, potassium persulfate (Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, and ion-exchanged water were mixed and purged with nitrogen gas to obtain an initially charged monomer emulsion. Also, the monomers, surfactant, polymerization initiator, and ion-exchanged water shown in "Dropped monomer emulsion" in Table 1 were mixed to obtain a dropped monomer emulsion, and then the dropped monomer emulsion was placed in the dropping funnel and purged with nitrogen gas. Under a nitrogen atmosphere, the initial monomer emulsion in the reaction vessel was heated from room temperature to 80°C over 30 minutes while stirring. While maintaining the temperature at 80°C, the monomer emulsion in the dropping funnel was gradually added dropwise to the reaction vessel over 3 hours. After the addition was complete, the mixture was stirred for 1 hour while maintaining the temperature inside the reaction vessel. The mixture was then filtered through a 200-mesh filter to obtain a pigment-free aqueous dispersion of fixing resin particles (acid value: 16 mg KOH / g, weight-average molecular weight: 750,000, solids concentration: 44.1%).

[0084] [Table 1]

[0085] Example 1 (Preparation of Water-Based Ink I1) To obtain the ink composition (total 100 parts) shown in Table 2, 7.1 parts (solid content) of Pigment Water Dispersion 1 obtained in Production Example 1 (solid content concentration: 22%, pigment: 15.4%, resin: 6.6%, acid value of pigment dispersion resin: 240 mgKOH / g), 4.0 parts (solid content) of fixing resin (solid content concentration: 44.1%), 5.0 parts of 1,5-pentanediol (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 20.0 parts of propylene glycol (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and polyether-modified silicone surfactant (TEGO (registered trademark) Wet 0.5 parts of "280" (active ingredient 100%), 0.5 parts of a polyether-modified silicone surfactant (BYK's "BYK349", active ingredient 100%), and 62.9 parts of ion-exchange water were added and thoroughly stirred, and the mixture was filtered through a membrane filter (Sartorius's "Minisart Syringe Filter", pore size: 5 μm, material: cellulose acetate) to obtain water-based ink I1. The average particle size of the resin particles in water-based ink I1 was 103 nm.

[0086] Examples 2 to 16 and Comparative Examples 1 to 3 Water-based inks I2 to I16 and IC1 to IC3 were obtained in the same manner as in Example 1, except that the ink compositions in Example 1 were changed to those shown in Table 2. The average particle diameters of the resin particles in the water-based inks are shown in Table 2.

[0087] The notations in Table 2 have the following meanings: 1,5-PD: 1,5-pentanediol (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., log P: 0.19) MFTG: Tripropylene glycol monomethyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., log P: 0.22) DEDG: Diethylene glycol diethyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., log P: 0.45) iBDG: Diethylene glycol isobutyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., log P: 0.64) PFG: Propylene glycol monopropyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., log P: 0.71) 1,2-HD: 1,2-hexanediol (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., log P: 0.85) PFDG: Dipropylene glycol monopropyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., log P: 0.88) BFG: Propylene glycol monobutyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., log P: 1.13) MFDG: Dipropylene glycol monomethyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., log P: 0.05) TEGO WET 270: Polyether-modified silicone surfactant (manufactured by EVONIK, "TEGO (registered trademark) Wet 270", HLB value 3.0, the number of repeating structural units represented by general formula (1) is 4.6, the number of repeating structural units represented by general formula (2) is 1.7, A is a trimethylene group, a is 0, b is 8.3, and R 1 is a methyl group) TEGO WET 280: Polyether-modified silicone surfactant (manufactured by EVONIK, "TEGO (registered trademark) Wet 280", HLB value 3.5, the number of repeating structural units represented by general formula (1) is 3.0, the number of repeating structural units represented by general formula (2) is 2.0, A is a trimethylene group, a is 0, b is 9.0, and R 1 is a methyl group) BYK345: Polyether-modified silicone surfactant (manufactured by BYK, HLB value 3.5, the number of repeating structural units represented by general formula (1) is 1.6, the number of repeating structural units represented by general formula (2) is 2.3, A is a trimethylene group, a is 0.36, b is 6.0, and R 1 is a hydrogen atom) BYK349: Polyether-modified silicone surfactant (manufactured by BYK, HLB value 4.0, the number of repeating structural units represented by general formula (1) is 1.3, the number of repeating structural units represented by general formula (2) is 1.7, A is a trimethylene group, a is 0.40, b is 9.2, and R 1 is a hydrogen atom) BYK3455: Polyether-modified silicone surfactant (BYK, HLB value 7.4)

[0088] The inks obtained in the examples and comparative examples were evaluated according to the following (1) to (4).

[0089] (1) Wetting and spreading properties In an environment with a temperature of 32°C, an inkjet printing evaluation device (manufactured by Tritec Corporation) equipped with a print head (manufactured by Kyocera Corporation, product name: KJ4B-EX1200, piezoelectric type) was filled with the water-based inks obtained in the Examples and Comparative Examples. The settings were print head voltage: 26 V, drive frequency: 30 kHz, ejected droplet volume: 3 pL, print head temperature: 32°C, and print head resolution: 1200 dpi. A 20 mm x 20 mm image was printed at a duty of 10% on a polyethylene terephthalate film ("Lumirror #25-T60" manufactured by Toray Industries, Inc.) (hereinafter referred to as "PET") as a low-liquid-absorbency printing substrate. The resulting prints were observed under an optical microscope, and the diameter of the ink dots was measured and recorded as the dot diameter. To print evenly on a PET surface with a resolution of 1200 dpi and an appropriate ink volume of 3 pL, a dot diameter of 30 μm was theoretically required. However, due to the impact accuracy and ejection error inherent in the inkjet head, a dot diameter of 30 μm may cause streaks (white spaces). Therefore, taking into account a 20% ejection error, we determined that a dot diameter of 36 μm or greater was practically usable for wetting and spreading the dots. The results are shown in Table 2. (Evaluation criteria) A: Dot diameter is 42 μm or more B: Dot diameter is 39 μm or more and less than 42 μm C: Dot diameter is 36 μm or more and less than 39 μm D: Dot diameter is 33 μm or more and less than 36 μm E: Dot diameter less than 33 μm

[0090] (2) Suppression of mottling Under the above printing conditions, a 100 mm x 100 mm solid image was printed on PET at a duty of 100%. The solid image on the obtained print was visually observed for the presence or absence of mottling, and the print quality was evaluated according to the following evaluation criteria. If the evaluation criteria were A to C, there was no problem in practical use. The results are shown in Table 2. (Evaluation criteria) A: No mottling is observed on the solid image, which is good. B: Slight mottling is observed on the solid image. C: Some mottling is observed on the solid image. D: Mottling is observed on the solid image. E: Excessive mottling is observed on the solid image.

[0091] (3) Suppression of white spots on printed materials Using the above printing conditions, a 20mm x 20mm solid image was printed on PET at 100% duty. If a surfactant with a low HLB value is not sufficiently dissolved in the solvent in the ink, white spots will appear in the solid image after drying. The percentage of white spots relative to the area of ​​the solid image was calculated using image analysis. Solid image prints with white spots were binarized using a print density value that was half the print density value of the solid image as a threshold value to calculate the area of ​​the white spots in the solid image. The percentage of white spots was calculated by dividing the area of ​​the white spots by the area of ​​the solid image. The smaller the percentage of white spots (%), the better the suppression of white spot occurrence in the print; if the white spots are less than 2.5% of the solid image, there is no practical problem. The results are shown in Table 2. (Evaluation criteria) A: No white spots on solid images B: White spots are less than 1% of the solid image C: White spots are 1% or more and less than 2.5% of the solid image D: White dots are 2.5% or more and less than 5% of the solid image E: White spots are 5% or more of the solid image

[0092] (4) Evaluation of ink storage stability Each of the water-based inks obtained in the examples and comparative examples was sealed in a screw tube (manufactured by Maruemu Co., Ltd.) and allowed to stand in a thermostatic chamber set at 70°C for 4 weeks. The average particle size was then measured to determine the "average particle size of the ink after storage," and the average particle size increase rate was calculated using the following formula. Average particle size increase rate (%) = [(average particle size of water-based ink after storage - average particle size of water-based ink before storage) / average particle size of water-based ink before storage] x 100 The average particle size of the water-based ink before and after storage was measured according to the description in "(4) Measurement of average particle size of water-soluble polyester dispersion and water-based ink" above. The smaller the value, the better the storage stability of the ink, and if the average particle size increase rate is less than 15%, there is no problem in practical use. The results are shown in Table 2. (Evaluation criteria) A: Average particle size increase rate is less than 5% B: Average particle size increase rate is 5% or more and less than 10% C: Average particle size increase rate is 10% or more and less than 15% D: Average particle size increase rate is 15% or more E: Aggregated and not measurable

[0093] [Table 2-1]

[0094] [Table 2-2]

[0095] Table 2 shows that the water-based inks obtained in the examples of the present invention have better ink wetting and spreading properties than the water-based inks obtained in the comparative examples, and are better at suppressing mottling and the occurrence of white spots on printed matter. On the other hand, Comparative Example 1 shows that when only one polyether-modified silicone surfactant with an HLB value of 1.0 or more and 7.0 or less is used, mottling suppression is poor; Comparative Example 2 shows that when the log P of the organic solvent (A) in the water-based ink is less than 0.10, wetting and spreading properties, mottling suppression, and suppression of white spots on printed matter are poor; and Comparative Example 3 shows that when one of the two surfactants (C) in the water-based ink has an HLB value higher than 7.0, wetting and spreading properties and mottling suppression are poor. If the HLB of the polyether-modified silicone surfactant is less than 1.0, the solubility of the polyether-modified silicone surfactant in the water-based ink will be poor, causing aggregation and the like, which is thought to result in poor suppression of white spots on printed matter and poor storage stability of the ink. [Industrial Applicability]

[0096] According to the present invention, it is possible to provide a water-based ink for inkjet printing that has excellent wetting and spreading properties on low-liquid-absorbent printing substrates, and is excellent in suppressing mottling and the occurrence of white spots on printed matter. Therefore, the water-based ink for inkjet printing of the present invention can be suitably used for printing on low-liquid-absorbent printing substrates for which water-based inks for inkjet printing have conventionally been used.

Claims

1. A water-based ink for inkjet printing on a low-liquid-absorbent printing substrate, comprising: the ink contains a pigment, an organic solvent (A), at least two polyether-modified silicone surfactants having an HLB value of 1.0 or more and 7.0 or less, and water; the organic solvent (A) has an octanol-water partition coefficient log P of 0.10 or more; Water-based ink for inkjet printing.

2. 2. The water-based ink for ink-jet printing according to claim 1, wherein the organic solvent (A) is at least one selected from the group consisting of 1,5-pentanediol, tripropylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, 1,2-hexanediol, dipropylene glycol monopropyl ether, and propylene glycol monobutyl ether.

3. 2. The water-based ink for ink-jet printing according to claim 1, wherein the content of the organic solvent (A) is from 0.1% by mass to 20% by mass.

4. 2. The water-based ink for ink-jet printing according to claim 1, wherein the content of each of the polyether-modified silicone surfactants is from 0.01% by mass to 2.0% by mass.

5. The water-based ink for ink-jet printing according to claim 1 , further comprising an organic solvent (B) other than the organic solvent (A).

6. 6. The water-based ink for ink-jet printing according to claim 5, wherein the organic solvent (B) is at least one selected from the group consisting of polyhydric alcohols and glycol ethers.

7. 2. The water-based ink for ink-jet printing according to claim 1, further comprising a fixing resin, wherein the fixing resin is at least one resin selected from the group consisting of a vinyl resin having a carboxy group, a polyurethane resin having a carboxy group, and a polyester resin having a carboxy group.

8. 2. The water-based ink for ink-jet printing according to claim 1, wherein the pigment is in the form of pigment-containing resin particles.

9. 9. A method for producing a water-based ink for ink-jet printing according to claim 1, comprising the step of mixing a pigment, an organic solvent (A), at least two polyether-modified silicone surfactants having an HLB value of 1.0 or more and 7.0 or less, and water, the organic solvent (A) has an octanol-water partition coefficient log P of 0.10 or more; A method for producing water-based inks for inkjet printing.

10. An inkjet printing method, comprising printing on a low liquid-absorbent printing substrate using the water-based ink for inkjet printing according to any one of claims 1 to 8.

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